The present invention relates to fibers containing oriented, crystalline or semi-crystalline polymer.
Composites contain a matrix resin that contains and is supported by a reinforcing fiber. Oriented polymer fibers are known to be useful in matrix resins. Typical oriented polymers include aramid fibers (commercially available under the trademark Kevlar.TM. from E. I. DuPont de Nemours & Co.); highly-oriented polyethylene fibers (commercially available under trademark Spectra.TM. from Allied-Signal Corp.); and polybenzazole fibers.
Each of those fibers presents several opportunities for improvement. First, the compressive strength of the fibers is typically small compared to their tensile strength and modulus. It would be desirable to improve that strength. Second, the fibers have a negative coefficient of thermal expansion in the axial direction and a positive coefficient of the thermal expansion in the radial direction. Such coefficients are suspected of causing troublesome microcracks in composites reinforced by Kevlar.RTM. polyamide fibers, and so it is desirable to minimize their effects in polybenzazole fibers. Third, it may be desirable to modify the behavior of fibers in specific environments, such as moisture uptake in hot wet environments, oxidative stability in oxidizing environments.